1. Field of the Invention
The present invention relates generally to the field of oxygen scavenging polymers. More particularly, it concerns multilayered packaging articles comprising an ethylene/vinyl alcohol copolymer (EVOH) oxygen barrier layer and an oxygen scavenging layer comprising an oxygen scavenging polymer, especially ethylene/methyl acrylate/cycloalkenylmethyl acrylate copolymers. The oxygen scavenging layer may also function as a tie layer useful in providing adhesion for the EVOH layer.
2. Description of Related Art
It is well known that limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf-life of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in a packaging system, the quality of the food product is maintained, and food spoilage is avoided. In addition such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and restocking. In the food packaging industry, several means for limiting oxygen exposure have already been developed, including modified atmosphere packaging (MAP), vacuum packaging and oxygen barrier film packaging. In the first two instances, reduced oxygen environments are employed in the packaging, while in the latter instance, oxygen is physically prevented from entering the packaging environment.
Another technique for limiting oxygen exposure involves incorporating an oxygen scavenger into the packaging structure. Incorporation of a scavenger in the package can scavenge environmental oxygen as it diffuses into the packaging structure, as well as scavenging residual oxygen present inside the package upon filling. Generally, the oxygen scavenger functions by irreversibly reacting with oxygen, and as a result, there exists a maximum amount of oxygen (the “oxygen scavenging capacity”) that the scavenger can scavenge, and therefore, there is a limit to the shelf life of the packaged article.
However, increasing the oxygen scavenging capacity by increasing the quantity of the oxygen scavenging polymer has the disadvantage of, typically, impairing the structural properties of the packaging article, as well as increasing the cost of materials and the cost or complexity of processing. Also, the oxygen scavenging rate should desirably be at least about as fast as the transmission rate of oxygen from the environment through the package wall.
From this, it will be recognized that limiting oxygen ingress into the packaging article is beneficial. If oxygen ingress into the packaging article is limited, less of the oxygen scavenging polymer will be required, and less can be used, thus improving the cost efficiency, physical properties, and processing of the packaging article. This is especially significant for products that are oxygen-sensitive but otherwise fairly resistant to spoilage, and are thus capable of shelf-lives on the order of at least months, or up to a year or more, such as beer or wine.
Ethylene/vinyl alcohol copolymer (EVOH) is widely known for having excellent barrier properties to gases (such as O2 and CO2) and other fluids, and has found wide use in packaging applications where barrier properties are desired. However, it is generally regarded as an insufficient oxygen barrier for packaging applications which require very strong oxygen barrier properties over a long period of time, such as beer packaging. Enhancement of the oxygen barrier properties of EVOH in a multilayered structure could be achieved by the use of an oxygen scavenging layer as described above.
However, in multilayer packaging articles, EVOH layers frequently delaminate from adjacent layers, and thus typically require the use of a tie layer or layers between the EVOH layer and other layers of the packaging article. Such tie layers typically do not provide any other benefit to the packaging article. An exception to this trend is nylon, which is known to bind EVOH and can provide other benefits to a packaging article.
Therefore, it would be desirable to have a packaging article comprising an EVOH layer and an oxygen scavenging layer or layers, which packaging article would be better suited for providing a very strong oxygen barrier over a long period of time than are packaging articles currently known. Also, it would be desirable for the oxygen scavenging layer or layers which are adjacent to the EVOH layer to function as tie layers in addition to their oxygen scavenging function.